This invention relates to a solid-state laser device for use in generating a laser beam by exciting a slab-shaped laser medium and a method of exciting the slab-shaped laser medium.
A conventional solid-state laser device of the type described has been disclosed by Robert L. Byer et al in U.S. Pat. No. 4,555,786. The laser device comprises a slab-shaped laser medium having a pair of principal surfaces and an excitation member for exciting the slab-shaped laser medium to generate a laser beam along a predetermined direction which will be called a first predetermined direction. The excitation member comprises a pair of excitation units opposite to each other and spaced apart from each other with a space gap therebetween. Each excitation unit comprises an excitation lamp extended along the first predetermined direction and a reflector surrounding the excitation lamp. The slab-shaped laser medium is disposed within the space between the excitation units with the principal surfaces directed towards the excitation lamps.
In this laser device, the slab-shaped laser medium is reciprocated within said space by the use of a driving member along a second predetermined direction transverse to the first predetermined direction. Such a reciprocating motion is reversely turned at two turning points. As a result, the slab-shaped laser medium is locally illuminated by the excitation lamps along the first predetermined direction in a stripe shape on both of the principal surfaces. This means that the slab-shaped laser medium is partially excited at an excited portion by the excitation lamps along the first predetermined direction to generate the laser beam through the excited region and is locally heated at the excited region by excitation light.
Inasmuch as the excited region is moved forwards and backwards along the second predetermined direction, as mentioned before, thermal energy is diffused all over the slab-shaped laser medium. Accordingly, it might be possible to make a thermal distribution uniform in the slab-shaped laser medium. Stated otherwise, a temperature rise may be reduced which might appear locally and entirely in the slab-shaped laser medium. This results in a reduction of a thermal expansion and a thermal distortion in the slab-shaped laser medium and enables use of laser glass which has a low thermal conductivity. In addition, such a uniform thermal distribution also enables pulse oscillation of a high repetition frequency.
According to the inventor's experimental studies, it has been found that the temperature distribution is not actually completely uniform in the slab-shaped laser medium. More particularly, a phenomenon has been found such that a temperature of the slab-shaped laser medium becomes high at portions adjacent to the turning points of the reciprocating motion as compared with the remaining portion of the slab-shaped laser medium. Therefore, it is difficult in practice to realize a complete uniform temperature distribution and to completely avoid the thermal expansion and the thermal distortion.